Process for purifying (hydro)halocarbon compositions

ABSTRACT

A process for treating a composition comprising one or more desired (hydro)halocarbons and one or more undesired halogenated hydrocarbon containing impurities so as to reduce the concentration of at least one undesired halogenated hydrocarbon containing impurity, the process comprising contacting the composition with an adsorbent comprising a carbon molecular sieve.

RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 14/786,318 filed 22 Oct. 2015, which is the U.S. National Phasecounterpart to PCT/GB2014/051259 filed 23 Apr. 2014.

BACKGROUND OF THE INVENTION

This invention relates to a process for reducing the concentration ofundesired impurities and, preferably, of undesired halogenated organiccompounds in (hydro)halocarbon compositions.

(Hydro)halocarbons are typically used as refrigerant or propellantmaterials. Over the last 20 years, the variety of (hydro)halocarbonsused in these applications has changed as it has been discovered thatsome such materials (such as difluorodichloromethane, R12) deplete theearth's ozone layer, while others (such as chlorodifluoromethane, R134a)have an unacceptably high action as a greenhouse gas.

The nature of the manufacturing processes of halogenated hydrocarbons issuch that one or more undesired or peripheral products are producedalongside a desired product in a product composition. The desiredproduct is then separated from the undesired or peripheral products by,say, distillation.

However, even after distillation, a desired product often includes tracequantities of the undesired or peripheral products, for example as aresult of the formation of an azeotropic mixture. It is also possiblethat substances used in other parts of the manufacturing process maycontaminate the product in trace quantities. Other separation techniquesmay also leave trace quantities of impurities in the desiredcomposition.

While in certain circumstances, such trace level contamination does notsignificantly affect the end use of the desired product, in others, suchas where the contaminant is toxic or has a relatively high globalwarming potential, where the end product may come into contact withmaterials which may be degraded by the contaminant or where the endproduct is for use in food or personal products, it is desirable tofurther reduce or eliminate the presence of those contaminants. It isparticularly desirable to control the content of low-level impurities incomposition intended for use in the medical and/or pharmaceutical field,such as those intended for use as a medical grade propellant.

It is known to use zeolites as molecular sieves to remove contaminantmaterials from (hydro)halocarbon products. US2005/0133360 describes theuse of zeolites to purify 1,1,1,2-tetrafluoroethane (HFC-134a) andchlorodifluoromethane (HCFC-22). WO2004/074225 describes the use ofzeolites for the removal of sulphur containing impurities from(hydro)halocarbons.

Zeolites provide a useful and effective means for separating componentsof a mixture when those components are of substantially different shapesand/or sizes. However, there is a need for a method and means forremoving impurities from a (hydro)halocarbon composition which iseffective when the undesired or peripheral component is of a similarshape and/or size to the desired component.

The listing or discussion of an apparently prior-published document inthis specification should not necessarily be taken as an acknowledgementthat the document is part of the state of the art or is common generalknowledge

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided aprocess for treating a composition comprising one or more desired(hydro)halocarbons and one or more undesired halogenated hydrocarboncontaining impurities so as to reduce the concentration of at least oneundesired halogenated hydrocarbon containing impurity, the processcomprising contacting the composition with an adsorbent comprising acarbon molecular sieve.

The inventors have surprisingly found that the use of carbon molecularsieves in the purification of (hydro)halocarbons provides for highlyselective removal of halogenated hydrocarbon impurities. The inventionprovides a marked improvement in such performance when compared with theuse of other molecular sieves having pore sizes of a similar order.

The contacting step of the process may be conducted in either the liquidor the vapour phase, but the liquid phase is preferred as it is moreeconomical to run.

Of course, the contacting step of the process should be conducted at atemperature that allows absorption to occur. The process preferably isperformed, at least in part, at a temperature of less than about 200°C., such as from about 5° C. to about 200° C. In some preferredembodiments, the process is performed, at least in part, at atemperature of about 20° C. to about 100° C. In still further preferredembodiments, the process is performed, at least in part, at atemperature of about 20° C. to about 60° C., e.g. around 40° C.

The contacting step of the method of the present invention may beconducted at any pressure sufficient to keep the components of thecomposition in the liquid or vapour phase, as appropriate. If theprocess is conducted in the liquid phase, it is preferably conducted atits autogeneous pressure, i.e. the pressure that the liquid itselfexerts, or higher if desired. If the process is conducted in the vapourphase, it is preferably conducted at a pressure of from 0.1 MPa to thesaturation pressure. For a given temperature, the saturation pressure ofa pure component is that pressure at which vaporisation of the liquidtakes place.

In some preferred embodiments, the process further comprises anadsorbent treatment step prior to the contacting step. Preferably, theadsorbent treatment step comprises heating the adsorbent to a maximumtemperature of at least 150° C., for example at least 200° C., at least250° C., at least 300° C., at least 350° C. or at least 400° C.

In some embodiments, the adsorbent treatment step comprises heating theadsorbent to the or a maximum temperature at a rate of 1° C./min to 100°C./min. Preferably, the adsorbent treatment step comprises heating theadsorbent to the or a maximum temperature at a rate of 10° C./min to 60°C./min. Preferably, the adsorbent treatment step comprises heating theadsorbent to the or a maximum temperature at a rate of 15° C./min to 40°C./min, e.g. around 20° C./min.

Preferably, the adsorbent treatment step is sufficiently long induration to ensure that any adsorbed species present on or in theadsorbent prior to use are removed. For example, the adsorbent treatmentstep may include maintaining the adsorbent at or around the or a maximumtemperature for between 1 second and 1 hour.

In some embodiments, the adsorbent treatment step comprises exposing theadsorbent to one or more inert gases, e.g. N₂ or one or more noblegases. In some embodiments, the exposure is performed before, during orafter the or a heat treatment step. Preferably, the exposure isperformed during at least part of the heat treatment step.

Preferably, the adsorbent has a mean pore diameter of around 0.5 Å toaround 20 Å, e.g. around 1 Å to around 10 Å. The pores may be sphericalor elliptical. In the case of elliptical pores the diameter may refer toeither dimension.

The process typically can be used to treat any (hydro)halocarbon that ismade by any method.

By the term “(hydro)halocarbon” we mean a compound that contains carbon,one or more halogen atoms and, optionally, hydrogen and/or oxygen. The(hydro)halocarbon may be saturated or unsaturated. Preferably, the(hydro) halocarbon has a carbon chain length of from one to four.

By the term “(hydro)haloethane” we mean a compound that contains twocarbon atoms, one or more halogen atoms and, optionally, hydrogen.

The composition to be treated may comprise one or more desired(hydro)halocarbons selected from halogenated alkanes, halogenatedalkenes and halogenated ethers.

Preferably, the composition to be treated comprises at least one desired(hydro)halocarbon selected from hydrofluoroalkanes,hydrochlorofluoroalkanes, chlorofluoroalkanes, perfluoroalkanes,perchloroalkenes, hydrochloroalkenes and (hydro)fluoroethers. Theprocess of the invention is particularly suitable for treatingcompositions in which the or each desired (hydro)halocarbon containsfluorine atoms as the only halogen atoms, for examplehydrofluoroalkanes, perfluoroalkanes and/or (hydro)fluoroethers. It isparticularly preferred that the or each desired compound is ahydrofluoroalkane.

By the term “hydrofluoroalkane”, we mean an alkane which contains onlycarbon, hydrogen and fluorine atoms.

By the term “hydrochlorofluoroalkane”, we mean an alkane which containsonly carbon, chlorine, fluorine and hydrogen atoms.

By the term “chlorofluoroalkane”, we mean an alkane which contains onlycarbon, chlorine and fluorine atoms.

By the term “perfluoroalkane”, we mean an alkane which contains onlycarbon and fluorine atoms.

By the term “perchloroalkene”, we mean an alkene which contains onlycarbon and chlorine atoms.

By the term “hydrochloroalkene”, we mean an alkene which contains onlycarbon, hydrogen and chlorine atoms.

By the term “(hydro)fluoroether”, we mean an ether which containscarbon, fluorine and oxygen atoms and, optionally, hydrogen atoms.

Desired hydrofluoroalkanes that may be purified include1,1,1,2-tetrafluoroethane (R-134a), 1,1-difluoroethane (R-152a),1,1,1-trifluoroethane (R-143a) or other mono-, di-, tri- ortetra-fluoroethanes. The use of the process of the present invention topurify 1,1-difluoroethane (R-152a) is particularly preferred.

Desired hydrochlorofluoroalkanes that may be purified include1,1-dichloro-1-fluoroethane (R-141b), 1-chloro-1,1-difluoroethane(R-142b), 1,1,1-trifluoro-2-chloroethane (R-133a),2,2-dichloro-1,1,1-trifluoroethane (R-123),2-chloro-1,1,1,2-tetrafluoroethane (R-124) or otherhydrochlorofluoroethanes.

Desired chlorofluoroalkanes that may be purified include1,2-dichloro-1,1,2,2-tetrafluoroethane (R-114) and1,1,1-trichloro-2,2,2-trifluoroethane (R-113a) or otherchlorofluoroethanes.

Desired perfluoroalkanes that may be purified include perfluoroethane(R-116).

The process can also reduce the concentration of inorganic and/ororganic sulphur containing impurities. It is particularly advantageousto use the process to reduce the concentration of organic sulphurcontaining impurities because these are typically more difficult toremove using standard techniques known to those skilled in the art.

By the term “organic sulphur containing impurities”, we mean compoundscontaining at least carbon and sulphur, optionally including other atomssuch as hydrogen and oxygen. Organic sulphur containing impurities thatcan be removed/reduced include (but are not limited to)dimethyldisulphide, ethanethiol, diethyldisulphide, carbon disulphideand carbonyl sulphide.

By the term “inorganic sulphur containing impurities”, we mean compoundscontaining at least sulphur, optionally including other atoms such ashydrogen and oxygen. Inorganic sulphur containing impurities that can beremoved/reduced include (but are not limited to) hydrogen sulphide,sulphur dioxide, sulphur trioxide and/or sulphuric acid.

The process of the present invention can be used to remove or reduce theconcentration of one or more undesired halogenated organic compounds.The process is particularly suitable for the removal/reduction ofhalogenated organic compounds containing one or two carbon atoms,although other undesired halogenated organic compounds may also beremoved. When the undesired halogenated organic compounds contain two ormore carbon atoms, they may be saturated or unsaturated.

By the term “undesired halogenated organic compounds” we mean undesiredcompounds that contain carbon, one or more halogen atoms and,optionally, hydrogen. The undesired halogenated organic compoundspreferably contain fluorine and/or chlorine and/or bromine, morepreferably fluorine and/or chlorine. Preferably, the undesiredhalogenated organic compounds comprise halogenated methanes, for examplehalomethanes, dihalomethanes or trihalomethanes.

DETAILED DESCRIPTION

The process typically removes at least 50% by weight, more preferably atleast 90% by weight and even more preferably at least 98% by weight ofthe halogenated hydrocarbon impurities. In some embodiments, the processreduces the concentration of halogenated hydrocarbon impurities tolevels at, around or below the limit of detection by smell and/or by gaschromatography.

The process does not necessarily reduce the concentration of every oneof the one or more undesired halogenated hydrocarbon impurities, but itmay do so.

Halogenated organic compounds that may be removed/reduced using theprocess of the present invention include (but are not limited to)chlorofluoromethanes, e.g chlorodifluoromethane (R-22) andchlorofluoromethane (R-31).

By the term “carbon molecular sieve”, we mean a molecular sievecomprising a substantially amorphous carbonaceous adsorbent withsubstantially uniform nanopores preferably of smaller than 20 angstromin mean pore diameter, such as those carbonaceous adsorbents produced bypyrolysis of polymeric precursor materials. As is understood by thoseskilled in art, such materials are distinct from activated carbon, whichis typically produced from vegetable materials such as coconut husks andtypically exhibits a far greater range of pore sizes.

If required, the adsorbent may be dried before use. Alternatively, theadsorbent may be used in the form it is obtained from the manufacturer.The preferred moisture level is less than about 1.5% by weight.

Typically, the process is conducted by circulating the composition to betreated through a polishing bed containing the adsorbent. The polishingbed may be a packed or fluidised bed, although a packed bed ispreferred.

The contact time depends on the amount of adsorbent being used and onits freshness. The skilled person would readily be able to determine asuitable contact time for a particular process.

The effectiveness of the adsorbent used in the process will deterioratewith time. The time that it takes for the adsorbent to deterioratedepends on a number of factors, such as the ratio of the amount ofadsorbent to the amount of the composition being treated.

The process of the present invention may further comprise the step ofregenerating the adsorbent after it has been contacted with the(hydro)halocarbon composition. For example, the adsorbent may beregenerated by contacting it with a heated nitrogen stream or by heatingit whilst nitrogen is passed over it.

It should be appreciated that a composition to be treated may becontacted with the adsorbent more than once. In such a process, thecomposition may be subjected to repeated contacts with one type ofadsorbent or subjected to contacts with more than one type of adsorbent.Repeated contact will further reduce the content of the one or moreundesired sulphur containing impurities and, if appropriate, of the oneor more undesired halogenated organic compounds.

Typically, the composition to be treated may be contacted with theadsorbent as many times as necessary to remove a sufficient quantity ofthe undesired halogenated hydrocarbons. The number of times that acomposition is contacted with the adsorbent depends on a number offactors, such as the freshness of the adsorbent and the initial level ofimpurities.

Typically, it is not necessary to subject the (hydro)halocarboncomposition to any additional treatment(s) prior to or after the processof the present invention in order to ensure that the concentration ofhalogenated hydrocarbon impurities is reduced.

However, if desired, the process can include one or more additionalpurifying steps, which may be conducted before and/or after the processof the present invention. The additional purifying steps may reduce theconcentration of undesired halogenated hydrocarbon impurities that arereduced/removed by the adsorbent.

The additional purifying steps may, optionally, reduce the concentrationof other undesired compounds, such as water or sulphur containingcompounds.

Any methods of purifying (hydro)halocarbons known in the art may be usedas additional purifying steps. For example, treatment with othermolecular sieves (e.g. zeolites) which are preferably acid stablemolecular sieves and may have a pore size of from 2 to 10 Å arepreferred. Additionally or alternatively, drying agents and/ordistillation techniques may be used.

Layers of different adsorbents and/or drying agents can be combinedwithin a single polishing bed. The order of the layers can be selectedby a person skilled in the art so as to provide the most efficienttreatment.

If required, distillation can be conducted before and/or after thecomposition to be treated is contacted with the adsorbent(s) and/ordrying agent(s) in the polishing bed.

According to another aspect of the invention, there is provided the useof au adsorbent comprising a carbon molecular sieve to reduce theconcentration of at least one undesired halogenated hydrocarbon impurityin a (hydro)halocarbon composition, such as those defined above.

According to yet another aspect of the present invention, there isprovided a composition that is substantially free of undesiredhalogenated hydrocarbon impurities obtainable by a process as describedabove.

Preferably, the composition is 1,1-difluoroethane (R-152a) or1,1,1,2-tetrafluoroethane (R-134a) or mixtures thereof that issubstantially free of undesired halogenated hydrocarbon impurities.

By the phrase “substantially free of undesired halogenated hydrocarbonimpurities”, we mean that the undesired halogenated hydrocarbonimpurities are present in an amount that is less than that which resultsin a quantity at around or below the amount detectable by gaschromatography. The skilled person will appreciate that the exact amountof undesired halogenated hydrocarbon impurities will depend on whichhalogenated hydrocarbon impurities were present in the compositionbefore the process is conducted because different compounds may bedetectable at different levels using gas chromatography. In someembodiments, “substantially free” refers to an impurity being present ina concentration of less than 15 ppm.

Compositions obtainable by a process as described above may be used as apropellant, especially as a medical and/or pharmaceutical propellant.Halogenated alkanes, such as hydrofluoroalkanes, for example1,1-difluoroethane (R-152a) and 1,1,1,2-tetrafluoroethane (R-134a) andmixtures thereof are suitable for this use.

Accordingly, in another aspect, the invention provides a pharmaceuticaldelivery device containing one or more pharmaceutically activesubstances and/or compositions and a composition obtainable by themethods described above.

Compositions obtainable by a process as described above may also be usedas a refrigerant, as a foam blowing agent, as a solvent and/or as a fireextinguishing agent.

For example, 1,1,1,2-tetrafluoroethane (R-134a) obtainable by a processas described above may be used as a solvent, for example as anextraction solvent for natural products, preferably as a flavour and/orfragrance extraction solvent.

In a further aspect, the invention provides an apparatus comprising acarbon molecular sieve and means to supply to said carbon molecularsieve a composition comprising one or more desired (hydro)halocarbonsand one or more undesired halogenated hydrocarbon containing impuritiesso as to reduce the concentration of at least one undesired halogenatedhydrocarbon containing impurity, wherein the undesired halogenatedhydrocarbon containing impurities comprises one or more of a mono-, di-or tri-halomethane, the desired (hydro)halocarbons are selected from

(i) 1,1,1,2-tetrafluorethane, 1,1,1-trifluoroethane, 1,1-difluoroethane,perfluoroethane or other mono-, di-, tri- or tetra-fluoroethanes;

(ii) 1,2-dichloro-1,1,2,2-tetrafluoroethane,1,1,1-trichloro-2,2,2-trifluoroethane, 1,1-dichloro-1-fluoroethane,1-chloro-1,1-difluoroethane, 1,1,1-trifluoro-2-chloroethane,2,2-dichloro-1,1,1-trifluoroethane (R-123),2-chloro-1,1,1,2-tetrafluoroethane and/or other(hydro)chlorofluoroethanes; and/or

(iii) (hydro)chloroethanes, (hydro)bromoethanes and/or(hydro)iodomethanes,

the apparatus being adapted and arranged to perform a process asdescribed above.

In a further aspect, the invention provides a method of providingcooling or heating using a heat transfer fluid comprising:

(i) 1,1,1,2-tetrafluorethane, 1,1,1-trifluoroethane, 1,1-difluoroethane,perfluoroethane or other mono-, di-, tri- or tetra-fluoroethanes;

(ii) 1,2-dichloro-1,1,2,2-tetrafluoroethane,1,1,1-trichloro-2,2,2-trifluoroethane, 1,1-dichloro-1-fluoroethane,1-chloro-1,1-difluoroethane, 1,1,1-trifluoro-2-chloroethane,2,2-dichloro-1,1,1-trifluoroethane (R-123),2-chloro-1,1,1,2-tetrafluoroethane and/or other(hydro)chlorofluoroethanes; and/or

(iii) (hydro)chloroethanes, (hydro)bromoethanes and/or(hydro)iodomethanes;

which method comprises a method of removing an undesired halogenatedhydrocarbon as described above. Preferably, the method of providingcooling is performed in a mobile air conditioning system.

In another aspect, the invention provides a heat transfer devicecomprising a heat transfer fluid comprising:

(i) 1,1,1,2-tetrafluorethane, 1,1,1-trifluoroethane, 1,1-difluoroethane,perfluoroethane or other mono-, di-, tri- or tetra-fluoroethanes;

(ii) 1,2-dichloro-1,1,2,2-tetrafluoroethane,1,1,1-trichloro-2,2,2-trifluoroethane, 1,1-dichloro-1-fluoroethane,1-chloro-1,1-difluoroethane, 1,1,1-trifluoro-2-chloroethane,2,2-dichloro-1,1,1-trifluoroethane (R-123),2-chloro-1,1,1,2-tetrafluoroethane and/or other(hydro)chlorofluoroethanes; and/or

(iii) (hydro)chloroethanes, (hydro)bromoethanes and/or(hydro)iodomethanes;

and an absorbent comprising a carbon molecular sieve. Preferably, theheat transfer device is a refrigeration system.

The present invention is now illustrated but not limited by thefollowing Examples.

EXAMPLE 1

A small sample (approximately 50 mg) of each adsorbent was accuratelyweighed into a 100 μl alumina crucible. The adsorbent was firstpre-treated by heating from 30-350° C. at 20° C./min under flowingnitrogen (125 ml/min). The sample was then cooled to 40° C. and exposedto 16.67% v/v HFC-152a in nitrogen for 2 hours with any uptake beingmonitored gravimetrically. Any adsorbent that showed negligible capacityfor HFC-152a was then further screened for methyl chloride adsorption inthe same manner.

The results are shown in Table 1, below.

The HFC-152a was of industrial grade and was sourced from Du Pont. Thismaterial was analysed and found to have the following composition:

Methyl Chloride = 28 ppm Unknown 1 = 5 ppm 254fb (CF₃CH₂CH₂F) = 7 ppmE-1131 (CHF═CHCl) = 1.2 ppm Balance HFC-152a (99.9588%)

COMPARATIVE EXAMPLES 1 TO 7

Various zeolite molecular sieves and a sample of activated carbon wastreated in the same manner as the carbon molecular sieve of Example 1and was exposed to HFC-152a in nitrogen in the same manner as in Example1, with any uptake being monitored gravimetrically. The adsorbent wasthen further screened for methyl chloride adsorption in the same manner.

The results are shown in Table 1, below.

TABLE 1 Capacity (% wt) Methyl Example Adsorbent Chloride HFC-152aComparative Chemviron — 17.53 Example 1 207ea Comparative UOP — 2.11Example 2 AW300 Comparative UOP — 2.84 Example 3 AW500 Comparative TOSOH4A — 3.81 Example 4 Comparative Sigma 3A — 2.36 Example 5 ComparativeSigma 4A — 2.98 Example 6 Comparative Sigma 5A — 18.37 Example 7 Example1 Union Showa 11.89 0.28 Carbon Molecular Sieve (CMS)

As can be seen from Table 1, the zeolite and activated carbon adsorbentsof Comparative Examples 1 to 7 were found to adsorb HFC-152a (some insignificant quantities). Surprisingly, the carbon molecular sieve ofExample 1 adsorbed little HFC-152a but selectively adsorbed methylchloride.

EXAMPLE 2

A 30 g sample of HFC-152a containing 28 ppm methyl chloride wasprepared. This sample was treated with 0.5 g Union Showa carbonmolecular sieve in a glass pressure cylinder at room temperature andautogenous pressure while being agitated with a magnetic stirrer. After8 hours of contact time, a sample of liquid HFC-152a was removed foranalysis by gas chromatography. The residual methyl chloride wasmeasured at 9 ppm.

EXAMPLES 3 TO 4

A small sample (approximately 35 mg) of each adsorbent was accuratelyweighed into a 100 μl alumina crucible. The adsorbent was firstequilibrated at 30° C. under nitrogen (100 ml/min) for 5 minutes, thenpre-treated by heating from 30-350° C. at 20° C./min under flowingnitrogen (100 ml/min) and held at 350° C. for 5 minutes. The sample wasthen cooled to 40° C. at −20° C./min, equilibrated under nitrogen (40ml/min) for 23.8 minutes and exposed to 16.67% v/v HFC-152a (60 ml/min)in nitrogen for 2 hours.

The supplied HFC-152a was in Examples 3 to 4 found to have a methylchloride concentration of 24 ppm. Uptake of HFC-152a and methyl chlorideto the absorbents was measured by thermogravimetric analysis. Theresults are shown in Table 2.

TABLE 2 Capacity (% wt) Methyl Example Adsorbent Chloride HFC-152aExample 3 Union Showa CMS 13.33 0.05 Example 4 Carboxen 569 10.79 3.56

EXAMPLES 5 TO 7

Samples of the absorbents were dried in a chamber furnace at 350° C. for12 h under nitrogen. 0.5000 g of the dried absorbents were then placedinto pressure vessels containing magnetic stirrer bars. Approximately 40ml HFC-152a was added to each pressure vessel, which was sealed andstirred at 1000 rpm for 7 hours.

The supplied HFC-152a was in Examples 3 to 4 found to have a methylchloride concentration of 24 ppm. The residual quantity of methylchloride in the remaining HFC-152a was measured by gas chromatography.The results are shown in Table 3.

TABLE 3 Residual MeCl Example Absorbent (ppm) Example 5 Union Showa CMS12 Example 6 Carboxen 569 10 Example 7 Carboxen 569 11

COMPARATIVE EXAMPLE 8

A sample of the Sigma 4A molecular sieve as used in Comparative Example6 was dried in a chamber furnace at 300° C. for 6 h under nitrogen (200ml/min). 0.5000 g of the dried absorbent was then placed into a pressurevessel containing a magnetic stirrer bar. Approximately 17 g HFC-152awas added to the pressure vessel, which was sealed and stirred at 1000rpm for 6 hours.

The supplied HFC-152a was in Comparative Example 8 found to have amethyl chloride concentration of 24 ppm. The residual quantity of methylchloride in the remaining HFC-152a was measured by gas chromatographyand was found to be 22 ppm.

Accordingly, it appears that carbon molecular sieve adsorbents may beused to selectively remove halogenated hydrocarbon impurities from(hydro)halocarbons. In particular, it appears that carbon molecularsieves may be unexpectedly adept at separating molecules which are ofvery similar effective diameters. Without wishing to be bound by anyparticular theory, it appears that the separation activity of carbonmolecular sieves is based on more than simply size exclusion; it ispostulated that surface interactions between the carbon molecular sieveand the composition to be separated may also play a part in the abilityof the sieve to absorb some molecules into pores of restricteddimensions.

Preferences and options for a given aspect, feature or parameter of theinvention should, unless the context indicates otherwise, be regarded ashaving been disclosed in combination with any and all preferences andoptions for all other aspects, features and parameters of the invention.

We claim:
 1. A composition that is substantially free of undesiredhalogenated hydrocarbon impurities, said composition obtained by aprocess of contacting a composition including the undesired halogenatedhydrocarbon impurities with an adsorbent comprising a carbon molecularsieve, wherein the undesired halogenated hydrocarbon containingimpurities comprises one or more of a mono-, di- or tri-halomethane, thedesired (hydro)haloethanes are selected from (i)1,1,1,2-tetrafluorethane, 1,1,1-trifluoroethane, 1,1-difluoroethane,perfluoroethane or other mono-, di-, tri- or tetra-fluoroethanes; (ii)1,2-dichloro-1,1,2,2-tetrafluoroethane,1,1,1-trichloro-2,2,2-trifluoroethane, 1,1-dichloro-1-fluoroethane,1-chloro-1,1-difluoroethane, 1,1,1-trifluoro-2-chloroethane,2,2-dichloro-1,1,1-trifluoroethane (R-123),2-chloro-1,1,1,2-tetrafluoroethane and/or other(hydro)chlorofluoroethanes; and/or (iii) (hydro)chloroethanes,(hydro)bromoethanes and/or (hydro)iodomethanes.
 2. The compositionaccording to claim 1 comprising 1,1-difluoroethane (R-152a),1,1,1,2-tetrafluoroethane (R-134a), or mixtures thereof that issubstantially free of undesired mono-, di- or tri-halomethaneimpurities.
 3. The composition according to claim 2 wherein thecomposition is substantially free of chloromethane.
 4. A compositioncomprising 1,1-difluoroethane as a major component that substantiallyfree of chloromethane.
 5. The composition according to claim 1 as apropellant, especially as a medical and/or pharmaceutical propellant. 6.The composition according to claim 5 as a medical and/or pharmaceuticalpropellant.
 7. The composition according to claim 1 used as arefrigerant, as a foam blowing agent, as a solvent and/or as a fireextinguishing agent.
 8. An apparatus comprising a carbon molecular sieveand means to supply to said carbon molecular sieve a compositioncomprising one or more desired (hydro)halocarbons and one or moreundesired halogenated hydrocarbon containing impurities so as to reducethe concentration of at least one undesired halogenated hydrocarboncontaining impurity, wherein the undesired halogenated hydrocarboncontaining impurities comprises one or more of a mono-, di- ortri-halomethane, the desired (hydro)halocarbons are selected from (i)1,1,1,2-tetrafluorethane, 1,1,1-trifluoroethane, 1,1-difluoroethane,perfluoroethane or other mono-, di-, tri- or tetra-fluoroethanes; (ii)1,2-dichloro-1,1,2,2-tetrafluoroethane,1,1,1-trichloro-2,2,2-trifluoroethane, 1,1-dichloro-1-fluoroethane,1-chloro-1,1-difluoroethane, 1,1,1-trifluoro-2-chloroethane,2,2-dichloro-1,1,1-trifluoroethane (R-123),2-chloro-1,1,1,2-tetrafluoroethane and/or other(hydro)chlorofluoroethanes; and/or (iii) (hydro)chloroethanes,(hydro)bromoethanes and/or (hydro)iodomethanes, the apparatus beingadapted and arranged to perform a process according to claim
 1. 9. Apharmaceutical delivery device containing one or more pharmaceuticallyactive substances and/or compositions and a composition according toclaim
 1. 10. The pharmaceutical delivery device according to claim 9further containing ethanol.
 11. A method of providing cooling or heatingusing a heat transfer fluid comprising: (i) 1,1,1,2-tetrafluorethane,1,1,1-trifluoroethane, 1,1-difluoroethane, perfluoroethane or othermono-, di-, tri- or tetra-fluoroethanes; (ii)1,2-dichloro-1,1,2,2-tetrafluoroethane,1,1,1-trichloro-2,2,2-trifluoroethane, 1,1-dichloro-1-fluoroethane,1-chloro-1,1-difluoroethane, 1,1,1-trifluoro-2-chloroethane,2,2-dichloro-1,1,1-trifluoroethane (R-123),2-chloro-1,1,1,2-tetrafluoroethane and/or other(hydro)chlorofluoroethanes; and/or (iii) (hydro)chloroethanes,(hydro)bromoethanes and/or (hydro) iodomethanes; which method comprisesa method of reducing or removing undesired halogenated hydrocarboncontaining impurities comprising one or more of a mono-, di- ortri-halomethane, as defined in claim
 1. 12. The method according toclaim 11 wherein the method of providing cooling is performed in amobile air conditioning system.
 13. A heat transfer device comprising aheat transfer fluid comprising (i) 1,1,1,2-tetrafluorethane,1,1,1-trifluoroethane, 1,1-difluoroethane, perfluoroethane or othermono-, di-, tri- or tetra-fluoroethanes; (ii)1,2-dichloro-1,1,2,2-tetrafluoroethane,1,1,1-trichloro-2,2,2-trifluoroethane, 1,1-dichloro-1-fluoroethane,1-chloro-1,1-difluoroethane, 1,1,1-trifluoro-2-chloroethane,2,2-dichloro-1,1,1-trifluoroethane (R-123),2-chloro-1,1,1,2-tetrafluoroethane and/or other(hydro)chlorofluoroethanes, and/or (iii) (hydro)chloroethanes,(hydro)bromoethanes and/or (hydro)iodomethanes; and an absorbentcomprising a carbon molecular sieve.
 14. The heat transfer deviceaccording to claim 13 wherein the heat transfer device is arefrigeration system.
 15. A heat transfer composition comprising acomposition according to claim 1.